The present invention relates to a finder device of a camera, and more particularly to a finder device having an auto-focus function.
For handy photography, cameras with a variable focusing device such as a zoom lens device have become common. In popular model cameras of this type, the photographic optical system is ever increasing in magnification power for the sake of more photographing fun. The finder optical system also implements a real image type zoom finder or the like so as to change in focal length along with the photographic optical system. That is, the finder optical system is configured to follow the movement of the photographic optical system. In close-ups, part of the lenses in the objective lens system of the finder optical system is/are moved to a predetermined position on the basis of the subject range information obtained through the auto-focus function for the photographic optical system. The focusing position of the objective lens system is thus adjusted to the focus position for close-ups.
Meanwhile, since increased powers of the finder optical system complicate the adjustment of diopter, there have been proposed finders capable of easy diopter adjustments. For example, Japanese Patent Laid-Open Publication No. 07005527 A discloses a finder of a camera comprising a photographic optical system and a finder optical system arranged independent of each other. In the camera finder, a first lens group in the finder optical system is continuously moved on the basis of the subject distance information output from distance measuring means provided in the camera, so that diopter variations and parallax resulting from changes in the distance to the subject are corrected continuously.
Japanese Patent Laid-Open Publication No. 08136983 A discloses a diopter-adjustable camera having a finder optical system including a display unit arranged in the finder optical system for displaying the relative relation to a subject image within the finder; an image-forming optical system for forming the subject image onto the display unit; a diopter adjustment optical system for introducing the beam of light transmitted and formed through the image-forming optical system and the display unit, and adjusting the same to a predetermined diopter; a ranging unit for measuring the distance to the subject; and a control unit for controlling the image-forming optical system based on the range measurement of the ranging unit. In the diopter-adjustable camera, the diopter adjustment optical system is driven with the subject image formed on the display unit.
Moreover, Japanese Patent Laid-Open Publication No. 08160501 A discloses a camera finder device having a finder auto-focus optical system and a finder zoom optical system on its optical path. In the finder, the magnification power of the finder ZOOM Optical system is detected by a finder control device. The finder control device then controls the finder auto-focus optical system in accordance with the above-mentioned magnification power as well as a ranging output for use in the focus adjustments to the photographic optical system, the output being selected from among a plurality of ranging points including the screen center.
Each of the conventional finder devices disclosed in the above publications, the finder optical system, driven on the basis of subject distance information obtained by the ranging unit provided in the photographic optical system, is inevitably affected by the state of the photographic optical system. That is, in the prevailing model cameras described above, the photographic optical system and the finder optical system are separate optical systems, and, therefore, the optical systems come into different states when temperature variations and the like occur. This means that driving the finder optical system on the basis of the range information concerning the photographic optical system can fail to focus the finder optical system. As a result, the photographer might have difficulty in recognizing the subject through the finder, possibly precluding the desired composition of a photograph.
In view of the foregoing, it is an object of the present invention to provide a camera finder device which can accurately obtain focus even when its finder optical system undergoes a change of state due to temperature and other causes.
As the technical means to achieve the foregoing object, the finder device of a camera according to the present invention is a finder device of a camera comprising a variable focusing device for changing the focal length of a photographic optical system. Here, the optical path of a finder optical system is branched out to form a focus detection system. Focus detecting means having a focus detection plane situated on the optical path of the focus detection system at an equivalent position to the focal plane of an objective lens system is provided. Driving means for moving an appropriate optical member of the finder optical system forward and backward along the optical axis is provided. The driving means move the appropriate optical member forward and backward on the basis of a detection signal from the focus detecting means, so that the finder optical system focuses on the focal plane.
When this finder is pointed at a subject, the subject image is formed on the focal plane as well as the focus detection plane of the focus detection system. Based on this subject image formed on the focus detection plane, the detection signal is output to the driving means, and an optical member constituting the finder optical system is moved forward/backward along the optical axis to adjust the subject image to be formed on the focus detection plane. Here, the optical member is positioned to focus on the detection plane by using a phase difference detection system or a hill-climbing contrast detection system, for example. The focus detection plane and the focal plane of the finder optical system are in equivalent positions to each other. Therefore, the in-focus state on the focus detection plane means the in-focus state on the focal plane which can be observed through an eyepiece lens to see the subject image in focus. Moreover, the in-focus state on the focal plane can be secured even when the finder optical system undergoes a change of state due to temperature variations and the like. The focus detection can be performed in synchronization with the ranging operation for the photographic optical system when the shutter release button is half pressed.
The finder device of a camera according to another aspect of the invention is the finder device wherein: the finder device is comprised of the objective lens system and an eyepiece lens system; the optical path is branched out in front of the eyepiece lens system to form the focus detection system; and the driving means move an appropriate optical member of the objective lens system forward/backward. That is, the camera comprising a variable focusing device for changing the focal length includes the finder device having an objective lens system and an eyepiece lens system. In the finder device, the optical path of the finder optical system is branched out in front of the eyepiece lens system to form the focus detection system. The focus detecting means has a focus detection plane situated on the optical path of the focus detection system, at an equivalent position to the focal plane. The driving means for moving an appropriate optical member of the objective lens system is provided. The driving means moves the appropriate optical member on the basis of a detection signal from the focus detecting means so that the finder optical system focuses on the focal plane.
The appropriate optical member of the objective lens system can be moved forward/backward along the optical axis by the driving means on the basis of the detection, signal output from the focus detecting means, to change the focusing position of the subject image. Therefore, the optical member is shifted to a position where the subject image comes into focus on the focus detection plane. Accordingly, on the focal plane situated at the equivalent position to the focus detection plane is also formed the subject image, which can be observed through the eyepiece lens system to see the in-focus subject image. In the finder device of a camera according to a further aspect of the invention, the driving means move a focus lens system in the objective lens system forward/backward. In the finder device of a camera according to another aspect of the invention, the driving means move the entire objective lens system forward/backward.
The optical member to be driven by the driving means on the basis of the detection signal of the focus detecting means may be the focus lens system in the objective lens system or the entire objective lens system. In either case, the subject image can be accurately formed on the focal plane so that the subject image is seen through the eyepiece lens system even when the finder optical system undergoes a change of state due to temperature variations and the like.
The finder device of a camera according to yet another aspect of the invention is a finder device of a camera comprising a variable focusing device for changing the focal length of a photographic lens. Here, a finder optical system having an objective lens system and an eyepiece lens system is provided. The optical path of the finder optical system is branched out in front of the eyepiece lens system to form a focus detection system. Focus detecting means having its focus detection plane situated on the optical path of the focus detection system is provided. Driving means for moving an appropriate optical member of the eyepiece lens system forward and backward along the optical axis is provided. The driving means move the appropriate optical member forward/backward on the basis of a detection signal from the focus detecting means so that the focus position of the eyepiece lens system is adjusted to the focus position formed by the objective lens system.
That is, the eyepiece lens system is driven by the driving means on the basis of the detection signal of the focus detecting means, so that the focus position of the eyepiece lens system is adjusted to the focus position formed by the objective lens system. In this manner, diopter correction is performed.
In the finder device of a camera according to another aspect of the invention, the driving means move a dioptric lens system in the eyepiece lens system forward/backward. In the finder device of a camera according to a further aspect of the invention, the driving means move the entire eyepiece lens system forward/backward.
Moving the dioptric lens system forward/backward provides the coincidence between the focus position of the eyepiece lens system and the focus position formed by the objective lens system, thereby performing diopter correction. Moving the entire eyepiece lens system also adjusts the focus position of the eyepiece lens system to that of the objective lens system to perform diopter correction.
In the finder device of a camera according to yet another aspect of the invention, the driving means moves a focus lens system in the eyepiece lens system forward/backward. In the finder device of a camera according to another aspect of the invention, the eyepiece lens system is provided with a dioptric lens system aside from the focus lens system.
The nature, principle, and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.